package servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

/**
 * 抽象类,通用servlet基础父类
 * Created by kevin on 2020/4/8.
 */
public abstract class BaseServlet extends HttpServlet{
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        /**
         * 1获取参数,辨别请求方法
         */
        String methodName = req.getParameter("method");
        try {
            /**
             * 2通过反射获取要调用的方法
             */
            Method method = this.getClass().getMethod(methodName,BaseServlet.class);
            try {
                /**
                 * 3执行方法
                 */
                String  result = (String) method.invoke(this,req,resp);
                /**
                 * 4处理返回值,返回格式(r:为重定向,f:为转发),null则什么也不做
                 */
                if(result==null || result.trim().isEmpty()){
                    return;
                }
                if(result.contains(":")){
                    int index = result.indexOf(":");//:号位置
                    String s = result.substring(0,index);//前缀
                    String path = result.substring(index+1);//后缀
                    if(s.equalsIgnoreCase("r")){
                        //重定向
                        resp.sendRedirect(req.getContextPath()+path);
                    }else if(s.equalsIgnoreCase("f")){
                        //转发
                        req.getRequestDispatcher(path).forward(req,resp);
                    }else {
                        throw new RuntimeException("不支持的操作:"+s);
                    }
                }else{
                    //转发
                    req.getRequestDispatcher(result).forward(req,resp);
                }
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            } catch (InvocationTargetException e) {
                e.printStackTrace();
            }
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        }
    }
}
